Shared bandwidth reservation in PL, ATM, FR and IP/MPLS networks

ABSTRACT

A method and a system for allocating restoration capacity in a network link in a communications network provides that a common pool of communication capacity is provisioned in a network link, such that the common pool of communication capacity includes spare capacity for new service and restoration capacity. A pool of pre-allocated communication capacity for future growth of at least one connection in the network link is also provisioned. The pool of pre-allocated communication capacity for future growth is available for restoration capacity, but not for spare capacity for new service. The communications network can be, for example, a private line (PL) network, a SONET-based network, an Asynchronous Transfer Mode (ATM)-based network, an Internet Protocol/MultiProtocol Label Switching (IP/MPLS)-based network or a frame relay (FR)-based network.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. Ser. No. 10/165,816 filedJun. 7, 2002, now U.S. Pat. No. 7,164,653, issued Jan. 16, 2007, and isincorporated by reference herein.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to telecommunications. More particularly, thepresent invention relates to a method and a system for reservingbandwidth for connection in a link in a communications network so thatthe reserved bandwidth is available for restoration.

2. Background of the Related Art

In Private Line (PL) networks, a customer can buy a point-to-pointconnection, such as an OC12c connection. The point-to-point connectioncould be formed from several sub-connections that have been co-routedand provisioned by the network over, for example, a number of switchesthat are connected by OC48 links. Such a connection is often referred toas a compound or bundled connection. In time, as the point-to-pointconnection traffic increases and/or when the customer adds moresub-connections to the compound connection, the point-to-pointconnection is required to grow in size. The increase can be hitless whenall of the OC48s links over which the point-to-point connection isrouted have sufficient spare bandwidth to accommodate the growth. Ifnot, the point-to-point connection may be required to be re-provisionedand another route is needed that has the necessary bandwidth on eachlink in the route. As the connection size increases, the likelihood thatthe increase will be hitless becomes less, and the task ofre-provisioning and rerouting the connection becomes more difficult.

When switch and link failures occur in a network, connections on afailed switch or link break and must be restored. Conventional networklinks maintain spare capacity in a common pool, or group, that is usedfor both service provisioning and for restoration of broken connections.Restoration is generally a temporary condition because when the failureis repaired, each restored connection is “reverted” from the restorationpath back to the original (service) path. The spare capacity, though,does not necessarily allow a connection to grow when needed becauseconnections are assigned to OC48s links in a way that maximizes thelikelihood of accommodating large new or restored connections, but canquickly leave little or no spare capacity for growth for a provisionedconnection.

FIG. 1 shows a functional block diagram of an exemplary communicationnetwork 100 having multiple links between switches. Communicationsnetwork 100 includes switches (SW) 101-104, links 111-118 and drop ports121-125. As shown in FIG. 1, SW 101 is connected to SW102 through links111-113. SW 102 is connected to SW 103 through links 114 and 115. SW 103is connected to SW 104 through links 116-118. SW 101 has drop ports 121and 122, SW 103 has drop port 124, and SW 104 has drop ports 123 and125. Switches 101-104 exchange a conventional link state advertisement(LSA) message to provide information about the topology (switches, linksand link metrics) in the network, as well as the total capacity and thespare capacity on each link. Links 111-118 are typically OC48 links, butcould also be either higher or lower speed links.

An exemplary connection 131 is shown in FIG. 1 connected between dropport 121 on SW 101 and drop port 123 on SW 104 through communicationsnetwork 100. The path of connection 131 through communications network100 includes link 112 between SW 101 and SW 102, link 114 between SW 102and SW 103, and link 118 between SW 103 and SW 104. Links 112, 114 and118 are, for example, OC-48 links, and connection 131 is, for example,an STS-12 connection that uses 12 STS-1 slots out of the 48 slots thatare available in each of links 112, 114 and 118. The remaining slots inlinks 112, 114 and 118 are used by other connections that are not shownor are spare (available). Another exemplary connection 132 is shown inFIG. 1 connected between drop port 124 on SW 103 and drop port 125 on SW104. The path of connection 132 through communications network 101includes link 118 between SW 103 and SW 104. Connection 132, forexample, could be an STS-3 connection that uses 3 STS-1 slots out of the48 total slots on link 118.

Suppose that, for example, the capacity pool for link 114 has a total of48 slots, and suppose that out of the 48 slots, only connection 131 isusing 12 slots of the 48 slots. FIG. 2 is a diagram representing theconventional capacity pools of link 114. Of the 48 slots of totalcapacity, 12 slots are in a service capacity pool 201 and 36 slots arein a spare capacity pool 202. The 36 slots of spare capacity in pool 202would be available for new service connections and/or for restoringconnections that fail elsewhere. For this example, SW 102 and SW 103would each send a LSA message to neighboring switches advertising thatlink 114 has 36 spare slots that are available. The LSA messages arepropagated to all other switches in the network using the conventionalmethod of LSA flooding.

Suppose that the total capacity pool for link 118 is also 48 slots.Connection 131 would use 12 slots of the total capacity and connection132 would use 3 slots of the total capacity for a total of 15 slots in aservice capacity pool. Thus, 33 slots in a spare capacity pool would beavailable on link 118 for new service connections and/or for restoringconnections that fail elsewhere. Switch 103 and SW 104 would each send aconventional LSA to the other switches advertising that link 118 has 33spare slots that are available.

FIG. 3 shows a flow diagram 300 of an exemplary conventional generalprocedure that is used for setting up a connection, whether for newservice or for restoration. At step 301, a request for a connection isreceived. At step 302, a network graph is constructed using informationcontained in the LSA messages. At step 303, links having insufficientspare capacity for the requested connection are pruned from the networkgraph. At step 304, the shortest path for the connection in theremaining network graph is determined using, for example, a well-knownalgorithm such as the Dijkstra algorithm. At step 305, the connection isset up along the shortest path determined in step 304. It should beunderstood that flow diagram 300 has been simplified to not includesteps that are performed when any of steps 301-305 cannot be performed.

In order to perform step 305 in FIG. 3, the switch originating theconnection sends out a setup message along the selected path. The setupmessage contains the selected path, as well as the bandwidth that isneeded by the connection and, possibly, other metric information. FIG. 4is a diagram representing a format arrangement 400 of a conventionalConnection Setup Message. Conventional Connection Setup Message formatarrangement 400 includes a field 401 containing information relating tothe path of a connection, a field 402 containing information relating tobandwidth required for the connection and other fields that are notshown in FIG. 4. The Connection Setup Message is processed by eachswitch in the selected path. When the connection can be established at aswitch—that is, the requested bandwidth is available—the switch forwardsthe setup message to the next switch in the selected path. Otherwise,the switch sends a (“crankback”) message to the originating switchindicating that the connection could not be established.

Returning to FIG. 1, suppose that it is desirable to increase the sizeof connection 131 from an OC12c to an OC24c. Growth can only occur onthe existing path when an additional 12 slots are free (i.e., in thespare capacity pool) on each of links 112, 114 and 118. Otherwise, thegrowth cannot be accommodated on the existing path and the connectionmust be re-routed on a different set of links, each of which must have24 spare slots available. Accordingly, there is a possibility thatconnection 131 might be required to be rerouted via a different set ofswitches that are not shown in FIG. 1. The reroute will cause atransmission hit while the connection is torn down over the originalpath and then set up on the new path.

Conventional connection routing attempts to maximize the fill ofpartially filled links and is based on the concept of leaving as large apool of spare capacity as possible on other links, thereby being able toaccommodate large connections. Consequently, connections establishedafter connection 131 has been established are likely to be routed onlinks used by 131 if those connections share part or the same entirepath with connection 131. Over time, the conventional approach uses upspare capacity on links used by connection 131 and reduces theprobability that there will be sufficient spare capacity for connection131 to grow. Thus, there may be sufficient capacity on other links, butgrowth of connection 131 causes a transmission hit.

One possible approach to overcome this disadvantage is to reserve, orpre-allocate, capacity for future growth of connection 131 whenconnection 131 is initially provisioned. Spare bandwidth could bereserved when connection 131 is originally set up by setting connection131 to be a larger connection than is initially needed. For example,suppose that when connection 131 is initially set up, an additional 12slots are reserved. The 48 total slots of capacity on link 114 are nowconfigured as 24 slots in the service capacity pool and 24 slots in thespare capacity pool. Only 24 slots of spare capacity are available fornew service connections and/or for restoring connections that failelsewhere. No other connection, including a restoration connection, canuse the capacity reserved by connection 131 because the reservedbandwidth is not currently available for any other purpose except forfuture growth of the connection. Thus, the reserved capacity that iswithin the service capacity pool is unused until the provisionedconnection requires the reserved bandwidth. Accordingly, a conventionalLSA message will advertise link 114 has 24 spare slots that areavailable.

What is needed is a way of reserving bandwidth for a single or acompound connection in a link in a communications network to allow forfuture growth of the connection, while making the reserved bandwidthavailable for restoration so that the reserved bandwidth is not wasted.

BRIEF SUMMARY OF THE INVENTION

The present invention provides a way of reserving bandwidth for a singleor a compound connection in a link in a communications network to allowfor future growth of the connection, while making the reserved bandwidthavailable for restoration so that the reserved bandwidth is not wasted.

The advantages of the present invention are provided by a method and asystem for allocating restoration capacity in a network link in acommunications network. A common pool of communication capacity isprovisioned in a network link, such that the common pool ofcommunication capacity includes spare capacity for new service andrestoration capacity. A pool of pre-allocated communication capacity forfuture growth of at least one connection in the network link is alsoprovisioned. The pool of pre-allocated communication capacity for futuregrowth is available for restoration capacity, but not for spare capacityfor new service. Accordingly, the communications network can be, forexample, a private line (PL) network, a SONET-based network, anAsynchronous Transfer Mode (ATM)-based network, an InternetProtocol/MultiProtocol Label Switching (IP/MPLS)-based network or aframe relay (FR)-based network. A connection for which the pool ofpre-allocated communication capacity for future growth has beenprovisioned can be a single or a compound connection. Provisioning ofthe pool of pre-allocated communication capacity can be performed inresponse to a received connection request or in response to a receivedconnection setup message. In that regard, the connection setup messageincludes information indicating whether the connection setup is for oneof a new service connection and a restoration connection and informationrelating to an amount of communication capacity reserved for theconnection setup. After the common pool of communication capacity andthe pool of pre-allocated communication capacity have been provisioned,a connection setup message is sent to another node within thecommunications network requesting a connection setup. Alternatively, alink state advertisement message is sent to another node within thecommunications network after the common pool of communication capacityand the pool of pre-allocated communication capacity are provisioned.The link state message includes information relating to restorationcapacity of the network link.

Another aspect of the invention provides a method and a system in whicha connection setup message is received, and it is determined whether theconnection setup message is for a new service connection or for arestoration connection. Communication capacity for a new serviceconnection is allocated from the common pool of communication capacitywhen the connection setup message is for a new service connection.Communication capacity for the restoration connection is allocated fromone of the common pool of communication capacity and the pool ofpre-allocated communication capacity for future growth when theconnection setup message is for a restoration connection.

Yet another aspect of the invention provides a method and a system forrestoring communications in a network in which a connection setupmessage is received for a restoration connection in a link of thenetwork, and communication capacity for the restoration connection isallocated from one of a common pool of communication capacity and a poolof pre-allocated communication capacity for future growth, such that thecommon pool of communication capacity includes spare capacity for newservice and restoration capacity for the network link, and the pool ofpre-allocated communication capacity for future growth is available forrestoration capacity, but not for spare capacity for new service.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is illustrated by way of example and by notlimitation in the accompanying figures in which like reference numeralsindicate similar elements and in which:

FIG. 1 shows a functional block diagram of an exemplary communicationnetwork having multiple links between switches;

FIG. 2 is a diagram representing the exemplary conventional capacitypools of a link in the communications network shown in FIG. 1;

FIG. 3 shows a flow diagram of an exemplary conventional generalprocedure that is used for setting up a connection;

FIG. 4 is a diagram representing a format arrangement for a conventionalConnection Setup Message;

FIG. 5 is a diagram representing exemplary capacity pools of a link inthe communications network shown in FIG. 1 according to the presentinvention;

FIG. 6 shows a flow diagram of an exemplary embodiment of a procedurethat is used for setting up a connection according to the presentinvention; and

FIG. 7 represents an exemplary format for a modified Connection SetupMessage according to the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention provides a method and a system for reserving, orpre-allocating, bandwidth for a single or a compound connection in alink in a telecommunications network for allowing for future growth ofthe connection and for making the reserved, or pre-allocated, bandwidthavailable for restoration so that the reserved bandwidth is not wasted.In that regard, the present invention provides pre-allocated bandwidthfor a connection in one of several predetermined sizes, such as OC6,OC12, OC24, OC48 and OC96. Additionally or alternatively, the presentinvention can provide pre-allocated bandwidth for a connection as aportion of one of several predetermined sizes. For example, a compoundconnection can be provisioned empty such that all of the pre-allocatedbandwidth initially is available for restoration purposes, therebyeasing provisioning and simplifying operation of support systems.Customers can buy an appropriately sized connection, such as a DS3, anOC3 or an OC12 connection. Smaller sized connections, such as a DS3 oran OC3 connection, can be combined into a larger connection, such as anOC12 connection. As the connection grows, the pre-allocated bandwidth isused by the connection. According to the present invention, any unusedpre-allocated bandwidth is available for restoration purposes, but isnot available for new service provisioning. Thus, the present inventionprovides two pools of spare capacity within a network link. The firstpool is a conventional spare capacity pool and the second pool is areserved, or pre-allocated, capacity pool. The conventional sparecapacity pool functions conventionally and is available for both newservice and restoration. The reserved capacity pool is available forgrowth of connections to which it was allocated and for restorationpurposes. Only connections that can be reverted are allowed use the poolof pre-allocated capacity because restoration is temporary in nature andthe restored circuits revert back relatively quickly to their homeroutes when a failure condition has been repaired.

The capacity pools that are associated with a network link areconfigured differently and used differently by the present invention. Toillustrate the differences between the present invention andconventional techniques, return to the earlier example in which capacitywas conventionally reserved, or pre-allocated, for future growth whenlink 114 was initially provisioned for connection 131. In the earlierexample, connection 131 was allocated 12 slots of service capacity and12 slots of reserve capacity for link 114. The 48 total slots ofcapacity on link 114 were then configured as 24 slots in the servicecapacity pool and 24 slots in the spare capacity pool. The 24 slots ofspare capacity were available for new service connections and/or forrestoring connections that fail elsewhere.

The present invention modifies the spare capacity pool for link 114 sothat 48 slots of capacity would be a pool of 12 slots of servicecapacity, a pool of 12 slots of reserved (pre-allocated) capacity and 24slots of spare capacity. FIG. 5 is a diagram representing exemplarycapacity pools 500 for link 114 according to the present invention forthis example. As shown in FIG. 5, the 48 slots of total capacity forlink 114 would be divided into a service capacity pool 501 that has 12slots allocated to connection 131, a reserved (pre-allocated) capacitypool 502 that has 12 slots pre-allocated for connection 131, and a sparecapacity pool 503. Both the service capacity pool 501 and the reservedcapacity pool 502 could also have slots allocated to other connections.Accordingly, 24 slots would be available as spare capacity (pool 503)and 36 slots would be available for restoration as the 24 slots that areavailable as spare capacity (spare capacity pool 503) plus the 12 slotsthat are reserved for growth of connection 131 (reserved capacity pool502).

Switch 102 would exchange a modified LSA message advertising 24 spareslots that are available for service and 36 spare slots for restorationon link 114. A modified LSA message, according to the present invention,includes additional information relating to restoration capacity.

FIG. 6 shows a flow diagram 600 of an exemplary embodiment of aprocedure that is used for setting up a connection, whether for newservice or for restoration, according to the present invention. At step601, a request for a connection is received. At step 602, a networkgraph is constructed using information contained in the LSA messages. Atstep 603, it is determined whether the connection request is for newservice or for restoration. If, at step 603, the request is for newservice, flow continues to step 604 where links having insufficientspare service capacity (i.e., no reserved capacity) for the requestedconnection are pruned from the network graph. Flow continues to step605, where the shortest path for the connection in the remaining networkgraph is determined using, for example, a well-known algorithm such asthe Dijkstra algorithm. At step 606, the connection is set up along theshortest path determined in step 605.

If, at step 603, it is determined that the connection request is forrestoration, flow continues to step 607 where links having insufficientspare restoration capacity (i.e., spare service capacity plus reservedcapacity) for the requested connection are pruned from the networkgraph. Flow continues to step 605. It should be understood that flowdiagram 600 has been simplified by not including steps that areperformed when any of steps 601-607 cannot be performed.

In step 606 in FIG. 6, a modified Connection Setup Message is sent alongthe path obtained by step 605. A modified Connection Setup Message,according to the present invention, includes information indicatingwhether the setup is for new service or restoration, and whether anybandwidth is reserved for growth. FIG. 7 represents an exemplary formatfor a modified Connection Setup Message 700 according to the presentinvention. The modified Connection Setup Message format 700 includes aconventional field 401 containing information relating to the path of aconnection and a conventional field 402 containing information relatingto bandwidth required for the connection. Additional fields provided bythe present invention include a field 701 containing aservice/restoration indicator and a field 702 containing informationrelating to the amount of bandwidth that is reserved for growth.

Every switch in the path selected for the connection processes themodified Connection Setup Message as follows. When service/restorationindicator field 701 indicates that the connection request is for newservice, then only the spare capacity pool for a link (pool 503) is usedfor the connection setup. The reserved capacity indicated in field 702(pool 502) is not considered for a new service connection setup. Thus,to successfully set up a new service connection, the spare capacity poolwithin a link (pool 503) must have sufficient available bandwidth tosatisfy both the bandwidth requested for the connection (field 402) andthe bandwidth reserved for growth of the connection (field 702). Whenthere is sufficient bandwidth in spare capacity pool 503, the amount ofbandwidth requested (402) by the modified Connection Setup Message isremoved from spare capacity pool 503 and placed in service capacity pool501. Any growth bandwidth for the connection (field 702) is also removedfrom spare capacity pool 503 and placed in the reserved capacity pool502.

When the indicator field of the modified Connection Setup Messageindicates that the connection is for restoration purposes, then both thespare capacity pool and the reserved capacity pool are considered by theswitch in response to the modified Connection Setup Message forproviding the requested bandwidth. The switch can allocate bandwidthfrom the spare capacity pool for the restoration connection beforeallocating the pre-allocated bandwidth from the reserved capacity poolin the event that there is insufficient bandwidth in the spare capacitypool for the restoration connection. Alternatively, the switch canallocate bandwidth from the reserved capacity pool before allocatingbandwidth from the spare capacity pool. When bandwidth for restorationis used from the reserved capacity pool regardless of the order ofallocation, the bandwidth is marked as “in use” and is not available for“pre-allocated” growth until released. There is no need to pre-allocatebandwidth for growth (field 702) for a restoration connection as theconnection is expected to revert back to the original path of theconnection before the connection grows.

In order to grow (or, conversely, contract) a connection, a modifiedConnection Setup Message according to the present invention is usedhaving new values in the appropriate fields of the message. Unless thetotal size of the connection is being changed, the sum of field 402containing the bandwidth needed and field 702 containing the reservedbandwidth for growth must be the same as when the previous modifiedConnection Setup Message for the connection was sent. Each switch in thepath processes the modified Connection Setup Message by appropriatelyadjusting the service capacity pool and the reserved capacity pool. Whenthe connection size is altered, each switch may need to allocateadditional bandwidth from the spare capacity pool (when the totalconnection size is increased) or release capacity into the sparecapacity pool (when the total connection size is decreased) along withappropriately modifying the service capacity pool and the reservedservice capacity pool.

While the invention has been described in terms of SONET connections, itshould be understood that the present invention applies equally to FR,ATM, IP or IP/MPLS networks in which the connection size is more fluidthan in PL-type networks, but also requires growth over time and issubject to similar OC48 (or other link size) limits.

While the invention has been described with respect to specific examplesincluding presently preferred modes of carrying out the invention, thoseskilled in the art will appreciate that there are numerous variationsand permutations of the above described systems and techniques that fallwithin the spirit and scope of the invention as set forth in theappended claims.

1. A method for allocating restoration capacity in a network link in acommunications network, the method comprising: provisioning a commonpool of communication capacity in a network link, the common pool ofcommunication capacity including spare capacity for new service andrestoration capacity; provisioning a pool of pre-allocated communicationcapacity for future growth of at least one connection in the networklink, the pool of pre-allocated communication capacity for future growthbeing available for restoration capacity and not for spare capacity fornew service; allocating communication capacity for a new serviceconnection from the common pool of communication capacity when aconnection setup message is for a new service connection; and allocatingcommunication capacity for a restoration connection from at least one ofthe common pool of communication capacity and the pool of pre-allocatedcommunication capacity for future growth when a connection setup messageis for a restoration connection.
 2. The method according to claim 1,wherein the communications network is a private line (PL) network. 3.The method according to claim 1, wherein the communications network is aSONET-based network.
 4. The method according to claim 1, wherein thecommunications network is an Asynchronous Transfer Mode (ATM)-basednetwork.
 5. The method according to claim 1, wherein the communicationsnetwork is an Internet Protocol/MultiProtocol Label Switching(IP/MPLS)-based network.
 6. The method according to claim 1, wherein thecommunications network is a frame relay (FR)-based network.
 7. Themethod according to claim 1, wherein at least one connection for whichthe pool of pre-allocated communication capacity for future growth isprovisioned is a compound connection.
 8. The method according to claim1, wherein the step of provisioning the pool of pre-allocatedcommunication capacity is performed in response to a received connectionrequest.
 9. The method according to claim 1, wherein the step ofprovisioning the pool of pre-allocated communication capacity isperformed in response to the receiving the connection setup message. 10.The method according to claim 9, wherein the connection setup messageincludes information relating to an amount of communication capacityreserved for the connection setup.
 11. The method according to claim 1,further comprising a step of sending a second connection setup messageto another node within the communications network requesting aconnection setup after the common pool of communication capacity and thepool of pre-allocated communication capacity are provisioned.
 12. Themethod according to claim 11, wherein the second connection setupmessage includes information indicating whether the connection setup isfor one of a new service connection and a restoration connection, andinformation relating to an amount of communication capacity reserved forthe connection setup.
 13. The method according to claim 1, furthercomprising a step of sending a link state advertisement message toanother node within the communications network after the common pool ofcommunication capacity and the pool of pre-allocated communicationcapacity are provisioned.
 14. The method according to claim 13, whereinthe link state message includes information relating to restorationcapacity of the network link.
 15. A system for allocating communicationcapacity in a network link in a communications network, the systemcomprising: a common pool of communication capacity in the network link,the common pool of communication capacity including spare capacity fornew service and restoration capacity; and a pool of pre-allocatedcommunication capacity for future growth of at least one connection inthe network link, the pool of pre-allocated communication capacity forfuture growth being available for restoration capacity and not for sparecapacity for new service, wherein communication capacity for a newservice connection is allocated from the common pool of communicationcapacity when a connection-setup message is for a new service connectionand communication capacity for a restoration connection from at leastone of the common pool of communication capacity and the pool ofpre-allocated communication capacity for future growth is allocated whenA connection setup message is for a restoration connection.
 16. Thesystem according to claim 15, wherein the communications network is aprivate line (PL) network.
 17. The system according to claim 16, whereinthe communications network is a SONET-based network.
 18. The systemaccording to claim 15, wherein the communications network is anAsynchronous Transfer Mode (ATM)-based network.
 19. The system accordingto claim 15, wherein the communications network is an InternetProtocol/MultiProtocol Label Switching (IP/MPLS)-based network.
 20. Thesystem according to claim 15, wherein the communications network is aframe relay (FR)-based network.
 21. The system according to claim 15,wherein at least one connection for which the pool of pre-allocatedcommunication capacity for future growth is provisioned is a compoundconnection.
 22. The system according to claim 15, wherein the pool ofpre-allocated communication capacity is provisioned in response to aconnection request received by a node of the communications networkconnected to the network link.
 23. The system according to claim 15,wherein the pool of pre-allocated communication capacity is provisionedin response to a connection setup message received by a node of thecommunications network connected to the network link.
 24. The systemaccording to claim 23, wherein the connection setup message includesinformation indicating whether the connection setup is for one of a newservice connection and a restoration connection, and informationrelating to an amount of communication capacity reserved for theconnection setup.